E-mail: ga03ali@yahoo.com بسم الله الرحمن الرحيم Comparative Analysis Of Airport Pavement Design Methods: Case Study for Khartoum New International Airport Prof Galal Ali – PhD, 1, Abdalla Khairy2, Tarig Mohamed2 and Ashraf Ahmed2 1Professor and Consultant Engineer, Sudan University of Science & Technology, E-mail: ga03ali@yahoo.com 2 Engineers, Private Sector Airports Arabia Conference Mövenpick Hotel, Kingdom of Bahrain. 5-6 May 2015

Recent Advances in Pavement Industry and Technology Super pave Mix Design Asphalt-Rubber in Hot Mix Design Mechanistic-Empirical Design Guide for both Rigid and Flexible Pavements Recycling of both Pavement Types Accelerated Loading Facilities to predict performance

BACKGROUND Pavement Design Governing Factors: Soil Sub-grade Strength California Bearing Ratio, CBR Resilient Modulus, MR Modulus of Subgrade Reaction, k Traffic Loading Equivalent Single Axle Load, ESAL Axle Load Distribution, ALD

Search for applicability, adoption and use of latest mechanistic asphalt and concrete airport pavement design methods, particularly in developing countries including the rich developing Gulf States. Required: improvements in terms of reduced life-cycle cost, shorter construction period, less disruption to residents and business, as well as safe and manageable field activities.

Pavement poor performance with premature failure in many cases, specially flexible pavements, a major concern with frequent and extensive occurrence making them unmanageable. Doubts and misinterpretation regarding their economics under various conditions when selecting a pavement type, particularly those countries predominantly use flexible pavements.

Premature Failure Obeid Khatim Road after afew Months of Construction. South-Bound 2 Outer Lanes have already been Rehabilitated

Such preference mainly relies on cost factor Two most crucial parameters that govern design of asphalt and Concrete Airport pavements are design traffic (million ESAL.) and soil subgrade strength in terms of CBR, Resilient modulus, MR and modulus of subgrade reaction, k

OBJECTIVES: Overview of popular flexible and rigid airport pavement design methods in a relative comparative manner. To apply procedures to conditions and data of Khartoum New International Airport for cost computations.

To determine sensitivity of the pavement design methods to the design parameters. Selection of optimal design method its cost estimate Study and compare using different paving materials and Structural and Economic evaluation for KNIA pavement design Method

DATA AND STATISTICS Khartoum state in Sudan: Population 8 X 106; Current international airport & domestic one The most Common pavement type and design method: flexible pavement designed by FAA semi-empirical method using CBR for soil subgrade strength, and the number of flight traffic operations KNIA Site Visit with Client (next slide)

Applying the following Procedures: The Current Study used 5 different methods for each of the 2 pavement types, Applying the following Procedures: Flexible Rigid AI (Analytical/ Nomograph) FAARFIELD LEDFAA COMFAA ACN/PCN PCA FAARFIELD LEDFAA COMFAA ACN/PCN FAA Method Suggested by Client and Consultant

Requirements for Flexible Pavement Design Methods Aircraft Characteristics Subgrade (CBR) Traffic Climate Method X6 X X1,2 N/A FAA X4 AI X6,7 X3,5 FAARFIELD LEDFAA COMFAA ACN/PCN 1Forcasted Traffic Mix 2Design Aircraft Concept 3Entire Traffic Mix 4Equivelent to DC-8 5Annual Growth 6Maximum Takeoff Weight 7Tire Pressure and Contact Area

Requirements for Rigid Pavement Design Methods Concrete characteristics Aircraft Characteristics Subgrade Strength (k) Traffic Climate Design Method X X6 X1,2 N/A FAA X6,7 X4 PCA X3,5 FAARFIELD LEDFAA COMFAA ACN/PCN 1Forcasted Traffic Mix 2Design Aircraft Concept 3 Entire Traffic Mix 4PresentOccasional or Frequent traffic 5Annual Growth 6Maximum Takeoff Weight 7Tire Pressure and Contact Area

Air Traffic Forecast KNIA Historical aircraft movement Data

Forecasted aircraft movement using time series method

KNIA Projected Flight Operations KNIA Traffic Forecast Analysis (KTFA) The results of forecasting show annual increase for aircraft operations by 2031 to reach 48.827 and 184,973 for international & domestic, respectively. . 1

KTFA-Continued To reach the movement of aircraft to the limit we need the proportion of annual increase for the movement of internal and external proportion of the increase expected it to serve that number of foreign trips is 3.5% for the Movement in 2011, the proportion of increase of the movement are up to 8.5% of the movement in 201

KNIA Design Traffic Mix

Determination of Mean Annual Air Temperature (MAAT) Temperature has great influence on the stress-strain characteristics of full-depth asphalt pavement and surface layer; thicknesses are increased as the average annual air temperature gets warmer. The table below shows the Mean Monthly Average Temperatures From Table below MAAT = 37 C

Soil Investigation: CBR Determination The area has rocky land characterized by high consistently and twice the capacity. All tests conducted by KNIA Unity Engineers indicated that the ground possed good natural resistance where they determined design CBR to be equal to 10 % suitable for use in the structural design of the Airport pavement. modulus of sub-grade (k): The k value was found using the equation above. With CBR =10, then k = 141.3 pci

Summary of Airport Pavement Design Using the required traffic data, conducting analysis of the design variables for KNIA and applying the various design methods resulted in a range of designs providing entirely different thicknesses. The design values are compared with the value suggested for KNIA . Summary:KNIA Structural Flexible Pavement Design :

Summary: KNIA Structural Rigid Pavement Design The results for flexible and rigid structural pavement designs show that FAA used for KNIA uneconomic over design compared with any of the methods adopted here. The difference was more pronounced for flexible pavement. Further study was undertaken to select the optimum method for each of flexible and rigid pavement

Comparison between the Design Methods: Flexible Pavement: 1- Effect of Subgrade Strength:

2- Comparing by Stabilized Base

3- Comparing Effect of Aircraft Departures on Thickness By FAA By AI

By COMFAA By FAARFIELD

By LEDFAA

Comparing Rigid Pavement Design Methods 1- Comparing by Modulus of Sub-Grade Reaction

2- Comparing By Stabilized Base

3- Comparing Effect of Aircraft Departures on Thickness By PCA By FAA

By COMFAA By LEDFAA

By FAARFIELD

Optimal Design Method (ODM) The study and analysis of 858 design results showed that the FAARFIELD is the best option available to design thus far with coefficient of determination not less than 0.995, It also followed a new methodology in the design (CDF) by using entire traffic mix for the design, It also can give the design life accurately for forecasted traffic mix, it also can give full depth design, As the results show it has the high sensitivity of the various paving materials and With all of this it give economically design.

Cost Considerations The Table and Fgure below show the cost of flexible and rigid pavements using the ODM (FAARFIELD) flexible rigid

Conclusions - Flexible Regarding pavement thickness design for KNIA case study, FAARFILED computer program was found to be the best option for airport pavement Structural design. The FAA design method does not yield reliable results for low subgrade strength, while becomes uneconomical design at higher subgrade strength . The structural design of airport pavements by LEDFAA & FAARFIELD computer program provide the most acceptable results.

Conclusions – Flexible, Continued Based on the results from a range of sub- grade strength values, the Asphalt Institute (AI) method gives lower thickness than other methods while not including most of new generation aircraft, as well as not accounting for the Stabilized-base option. COMFAA program exhibited being insensitive to stabilized base. When compared using stabilized base, LEDFAA and FAARFIELD computer programs showed negligible average difference.

Conclusions - Rigid FAA method was found to be insensitive to stabilized-base material providing same slab thickness. On the other hand, LEDFAA and FAARFIELD showed high sensitivity to varying base material. FAA method resulted in average thickness difference ranging between 9 and 3 inches compared with PCA, LEDFAA, COMFAA and FAARFIELD, respectively confirming the method is relatively not effective. The PCA method gives design for the surface layer only, while base and subbase thicknesses are assumed.

Conclusions – Rigid, Continued For KNIA pavement thickness design, the same first conclusion for Flexible pavement applies, that is FAARFILED is the best option The PCA method showed a differing trend, giving larger thicknesses than FAA values for medium and high subgrade strength, and small thicknesses than FAA method for low strength.

Conclusions Rigid, Continued The pavement structure appeared to be more sensitive to departure levels than any other parameter. Results showed that FAARFIELD computer program give accurate results with coefficient of determination not less than 0.995.

Recommendations Modern technology advances need to be adopted in order to keep design development up-to-date. Conduct specialized research to develop new design variables to improve design methods. Introduce new forecasting techniques for aircraft traffic growth rates. Adhere to using entire traffic mix for airfield design rather than relying on design aircraft. Replace semi-empirical design charts, typical of FAA method, by mechanistic design procedures. Using stabilized base instead of crushed aggregate is preferred for airports weighing weight more than 100 kips to.

Recommendations Continued FAAFAIELD design method is Recommend for adoption by Sudan Civil Aviation Due to lack of experience and qualified staff, it is recommended to establish research institutes specialized in airport engineering. As was justified technically & economically in earlier studies on highway pavements, use of rigid pavement should be encouraged. The AI method is stressful mathematically in the design where it can be dispensed with FAARFIELD for full depth design

Acknowledgements Eng Muram Mohamed, Lecturer at University of Science and Technology; Eng Mohamed H Ismael Project Implementation Unit, Air Traffic Control and Aviation Security Departments of Khartoum New International Airport

Thank you; Questions?